Field of the Invention
The present invention relates to a printing apparatus and a calibration method thereof, and particularly to, for example, a printing apparatus capable of detecting the distance from a printhead to a print medium using a sensor, and a calibration method of the sensor.
Description of the Related Art
Conventionally, an inkjet printing apparatus (to be referred to as a printing apparatus hereinafter) includes a number of sensors according to various purposes to, for example, raise the quality or resolution of a printed image or improve operability. For example, the printing apparatus includes a sensor that detects the width of a print medium such as print paper set on the printing apparatus, a sensor that detects the density of a print adjustment pattern printed on print paper, and a ranging sensor that detects the thickness of print paper.
By the way, minute ink particles, which do not land on a print medium and are called an ink mist, are dispersed from ink discharged from an inkjet printhead (to be referred to as a printhead hereinafter) used in the printing apparatus. The ink mist is dispersed together with an air flow created as the air in the apparatus is disturbed by, for example, the movement of a carriage with the printhead, adheres to various places, and contaminates the interior of the apparatus. The ink mist may adhere to the ranging sensor configured to detect the distance between print paper and the printhead, an encoder sensor and a linear scale configured to detect the position of the carriage, or an encoder sensor and a code wheel configured to detect the rotation amount of a print medium conveyance roller. When the ink mist adheres, detection errors may occur in the detection units, resulting in a failure in image printing or the operation of the apparatus.
Conventionally, an optical ranging sensor is used in the printing apparatus. Ranging detection using the sensor is generally performed in the following way. That is, the emitting element of the sensor irradiates a measurement target with light. A photoreception element receives the light reflected by the measurement target. The distance to the measurement target is obtained using triangulation.
In some conventional printing apparatuses, a ranging sensor is mounted on a carriage that includes a printhead and reciprocally moves. In the ranging sensor, a plurality of photoreception elements provided in the sensor irradiate a measurement target with light, receive the light reflected by the measurement target, and measure the ratio value of the intensity of the reflected light to that of the output light. The distance up to print paper is calculated based on a reference result of the measurement result and a distance information reference table that shows relationship between a light intensity and a distance detected by a calibration reference board mounted on the printing apparatus (see Japanese Patent Laid-Open No. 2008-265058).
In the prior art, however, if an ink mist adheres to the sensor over time, the degrees of adhesion to the plurality of emitting elements and photoreception elements are not always equal. In addition, if the degrees of adhesion to the plurality of photoreception elements are not equal, the ranging accuracy lowers. To solve this problem, a method of calibrating the ranging sensor as needed using a calibration reference board may be used. However, this arrangement greatly increases the cost of the apparatus.